A free society needs people with consciences. The vast majority of people must obey the law voluntarily. If people don’t conform themselves to the law, someone will either have to compel them to do so or protect the public when they do not. It costs a great deal of money to catch, convict, and incarcerate lawbreakers — not to mention that the surveillance and monitoring of potential criminals tax everybody’s freedom if habitual lawbreakers comprise too large a percentage of the population.

The basic self-control and reciprocity that a free society takes for granted do not develop automatically. Conscience development takes place in childhood. Children need to develop empathy so they will care whether they hurt someone or whether they treat others fairly. They need to develop self-control so they can follow through on these impulses and do the right thing even if it might benefit them to do otherwise.

All this development takes place inside the family. Children attach to the rest of the human race through their first relationships with their parents. They learn reciprocity, trust, and empathy from these primal relationships. Disrupting those foundational relations has a major negative impact on children as well as on the people around them. In particular, children of single parents — or completely absent parents — are more likely to commit crimes.

Without two parents, working together as a team, the child has more difficulty learning the combination of empathy, reciprocity, fairness, and self-command that people ordinarily take for granted. If the child does not learn this at home, society will have to manage his behavior in some other way. He may have to be rehabilitated, incarcerated, or otherwise restrained. In this case, prisons will substitute for parents.

I am reading her book Love and Economics right now, and this argument is in the first couple of chapters, which is how I found this article.